I would find it helpful to see the Read/Unread status of discussions posts from within SpeedGrader. My discussions take place over the course of a few days, and I grade cumulatively during each of those days. It would speed things up for me to scroll to the next Unread post for each student.
There is a similar discussion going on in Grading Discussion in the Discussion Stream. The changes being discussed there might subsume this request. But in case that idea doesn't go anywhere, I've posted this idea here.